materials, each size of aggregate, water, and admixtures shall be
continuously controlled. The aggregate weights and amount of added water
shall be adjusted as necessary to compensate for free moisture in the
aggregates. A report shall be prepared indicating type and source of
cement used, type and source of pozzolan or slag used, amount and source of
admixtures used, aggregate source, the required aggregate and water weights
per cubic yard, amount of water as free moisture in each size of aggregate,
and the as-mixed aggregate and water weights per cubic meter yard for each
class of concrete placed during plant operation.
3.10.2.6
Concrete
a. Conventional Concrete Slump Testing - At least two slump tests
shall be made in accordance with ASTM C 143/C 143M on each conventional
concrete mixture, including bedding mortar produced during each 8-hour
period or less of concrete production each day. Additional tests shall
be made when excessive variation in workability is reported by the
placing foreman or Government inspector. The result of each test for
each mixture shall be plotted on a control chart on which the upper and
lower limits are set as specified in paragraph PROPORTIONS. The range
shall be plotted on a control chart on which the upper control limit is
50 mm 2.0 inches. Samples for slump shall be taken at the mixer,
however the Contractor is responsible for delivering the concrete to
the placement site at the stipulated slump. If the Contractor's
materials or transportation methods cause slump loss between the mixer
and the placement, samples shall be taken at the placement site as
often as required by the Contracting Officer.
b. Slump Corrective Action - Whenever points on the control chart
approach the upper or lower control limits, an adjustment shall be made
in the batch weights of water and fine aggregate. The adjustments are
to be made so that the total water content does not exceed that amount
specified in the mixture proportions provided by the Contracting
Officer based on the free water available with the aggregates and that
amount of water batched. If the adjustments to the batch weights of
water and aggregates do not satisfactorily produce the required slump,
the Contracting Officer may adjust the mixture proportions if the
fine-aggregate moisture content is found to be stable and within the
required limits. When a single slump is outside the control limits,
such adjustment is mandatory. As soon as practical after each
adjustment, another test shall be made to verify the correctness of the
adjustment. Whenever two consecutive individual slump tests, made
during a period when there was no adjustment of batch weights, produce
a point on the control chart for range above the upper control limits,
the slump shall be considered to be out of control, the concreting
operation halted, and the additional testing for aggregate moisture
content required shall be undertaken, and action taken immediately to
correct the problem.
c. Air Content - At least one test for air content of conventional
concrete shall be made on a randomly selected batch of each concrete
mixture produced during each 8-hour period of concrete production.
Additional tests shall be made when excessive variation in workability
is reported by the placing foreman or Government inspector. Tests
shall be made in accordance with ASTM C 231. The average of each test
for each mixture shall be plotted on control charts on which the
average percent and upper and lower limits are set in accordance with
paragraph PROPORTIONS. The range between two consecutive tests for
each mixture shall be plotted on a control chart on which the upper
SECTION 03701
Page 63
Previous Page
